The present invention relates generally to a coupling structure of extensible shafts used for a steering apparatus, etc., of an automobile, and more particularly to a coupling structure of extensible shafts, which is capable of easily adjusting a sliding resistance between an inner shaft and an outer shaft even after the outer shaft has been assembled to the inner shaft by spline-fitting.
One type of a steering apparatus of an automobile is a telescopic type steering apparatus capable of adjusting an axial length of a steering shaft corresponding to a sitting posture and a physique of the driver.
In this telescopic type steering shaft, an outer shaft connected via a universal joint, etc., to a steering wheel is spline-fitted to an inner shaft connected via a universal joint, etc., to a gear, etc., on the side of the wheels. With this configuration, a length of the steering shaft can be adjusted in such a way that the outer shaft slides on the inner shaft in the axial direction.
The telescopic type steering shaft has drawbacks wherein there is a scatter in slide resistance between the inner and outer shafts depending on the shafts as products when the outer shaft is spline-fitted to the inner shaft and thus assembling these shafts, and a xe2x80x9cbacklashxe2x80x9d occurs between the inner and outer shafts. Therefore, generally the slide resistance between the two shafts is adjusted by controlling a thrusting force acting in the radial direction on the inner shaft against the outer shaft, and the xe2x80x9cbacklashxe2x80x9d between the two shafts is thus prevented.
According to, e.g., Japanese Patent Application Laid-Open Publication No. 11-198822, an adjustment screw and a wedge-shaped diameter-expanding member are provided within the inner shaft. When this adjustment screw is intruded in the axial direction, the wedge-shaped diameter-expanding member expands its diameter in the radial direction, and the thrusting force acting in the radial direction on the inner shaft against the outer shaft is thus adjusted. The slide resistance between the inner and outer shafts can be thereby adjusted, and the xe2x80x9cbacklashxe2x80x9d between these two shafts can also be prevented.
Further, according to Japanese Patent Application Laid-Open Publication No. 2-87116, similarly when the adjustment screw is intruded in the axial direction within the inner shaft, a diameter of a tapered portion of a collar (diameter-expanding member) is expanded in the radial direction, thereby adjusting the thrusting force acting in the radial direction on the inner shaft against the outer shaft. With this adjustment, the slide resistance between the two shafts can be adjusted, and the xe2x80x9cbacklashxe2x80x9d between these two shafts can also be prevented.
In the telescopic type steering shaft disclosed in both of the Publications, however, the thrusting force is controlled by moving the adjustment screw in the axial direction which is provided within the inner shaft, and the slide resistance is thus adjusted. Hence, the outer shaft is spline-fitted to the inner shaft and, after thus assembling these shafts, an operation of moving the adjustment screw in the axial direction within the inner shaft is comparatively hard, resulting in a poor operation efficiency. Further, even when adjusting the thrusting force before the assembly, it is comparatively difficult to modify the adjusted thrusting force after the assembly.
It is an object of the present invention, which was devised under such circumstances, to provide a coupling structure of extensible shafts that is capable of easily adjusting a slide resistance between an inner shaft and an outer shaft even after assembling the inner and outer shafts by getting the outer shaft spline-fitted to the inner shaft, and of surely preventing a xe2x80x9cbacklashxe2x80x9d between the two shafts.
To accomplish the above object, according to one aspect of the present invention, a coupling structure of extensible shafts extensible in an axial direction and coupled so as to be incapable of rotating, is characterized by comprising an inner shaft, an outer shaft fitted to the inner shaft so as to be incapable of rotating and slidable in the axial direction, and an adjustment screw movable in radial direction of the two shafts, wherein the adjustment screw is moved in the radial direction after the outer shaft has been fitted to the inner shaft, and a thrusting force in the radial direction between the two shafts is thus adjusted.
A coupling structure of extensible shafts according a second aspect of the present invention is characterized in that the outer shaft is hollowed and has a through-hole formed in the radial direction, the inner shaft is hollowed and has a female thread formed in the radial direction facing to the through-hole, and the adjustment screw penetrates the through-hole, meshes with the female thread, moves in the radial direction of the inner shaft, then thrusts an inner peripheral portion of the inner shaft, and thus adjusts a thrusting force between the two shafts.
A coupling structure of extensible shafts according to a third aspect of the invention is characterized in that the outer shaft is hollowed and has a through-hole formed in the radial direction, the inner shaft is hollowed and has a through-hole formed in the radial direction facing to the through-hole, a screw member formed with a female thread in the radial direction that meshes with the adjustment screw is provided inwardly of the inner shaft, and the adjustment screw penetrates the through-hole, meshes with the female thread of the screw member, moves in the radial direction of the inner shaft, then thrusts an inner peripheral portion of the inner shaft, and thus adjusts a thrusting force between the two shafts.
A coupling structure of extensible shafts according to a fourth aspect of the invention is characterized by further comprising a receiving member for supporting a front side end of the adjustment screw.
A coupling structure of extensible shafts according to a fifth aspect of the invention is characterized in that the screw member and the receiving member are integrally formed through a connecting portion that is elastically deformable in the radial direction of the inner shaft.
A coupling structure of extensible shafts according to a sixth aspect of the invention is characterized in that the receiving member includes two side walls facing to each other in the axial direction of the inner shaft and extending in a direction substantially right-angled to the axial direction, and a bottom portion having a swelling, formed at its center in the axial direction to integrally connect the side walls, upon which a front side end of the adjustment screw impinges, the two side walls holding the screw member,
the swelling is thrust as the adjustment screw moves in the radial direction, the two side walls move in the radial direction of the inner shaft while slidably holding both of side surfaces of the screw member in the axial direction, the screw member and the receiving member thrust the inner peripheral portion of the inner shaft, and a thrusting force between the two shafts is thus adjusted.
A coupling structure of extensible shafts according to a seventh aspect of the invention is characterized in that the screw member has a brace extending towards both sides in the axial direction from the central portion formed with the female thread, then bent outwards in the radial direction and impinging on an inner peripheral surface of the inner shaft, the receiving member has a brace extending towards both sides in the axial direction from the central portion for supporting the front side end of the adjustment screw, then bent in the radial direction on the opposite side to the brace of the screw member, and impinging on an inner peripheral surface of the inner shaft, and both of the braces are given a spring property.
A coupling structure of extensible shafts according to an eighth aspect of the invention is characterized in that a pair of the screw member and the receiving member are provided at a predetermined interval in the axial direction of the inner shaft, and the screw member and the receiving member are integrally formed at the predetermined interval through an elastically deformable connecting portion.
A coupling structure of extensible shafts according to a ninth aspect of the invention is characterized in that the inner shaft has at least a couple of elongate holes formed in the vicinity of a portion provided with the adjustment screw and extending in the direction parallel to the axial direction of the inner shaft, and the elongate holes function to lessen a rigidity of the inner shaft.
A coupling structure of extensible shafts according to a tenth aspect of the invention is characterized in that the outer shaft is hollowed, and the inner shaft is fitted in the outer shaft, a ring-like member having a screw portion formed with a female thread in the radial direction that meshes with the adjustment screw and a receiving portion, provided in a position facing in the radial direction to the screw portion, for supporting the outer shaft, is provided along a periphery of the outer shaft at a portion where the inner and outer shafts are fitted to each other, and the adjustment screw meshes with the female thread of the screw portion of the ring-like member and thus moves inwards in the radial direction of the outer shaft, a front side end of the adjustment screw and the receiving portion thereby thrust the outer shaft in an inside-diametrical direction, and a thrusting force acting inside in the radial direction of the outer shaft is thus adjusted.